Field of the Invention
The present invention relates to a production method of morpholino oligonucleotide, and morpholino nucleotide used as a starting material of the production method.
Discussion of the Background
Morpholino oligonucleotide is a compound attracting attention for its use as an antisense oligonucleotide, since it shows high affinity for DNA and RNA, resistance to various nucleases, stability in vivo and low toxicity (see non-patent document 1).
As a production method of morpholino oligonucleotide, a solid phase synthesis and a liquid phase synthesis have been reported (see non-patent document 2, patent documents 1-5).
The solid phase synthesis is advantageous from the aspect of speed since it enables automatic synthesis. On the contrary, it is not suitable for industrial large scale synthesis since scaling-up is limited due to facility restriction, and low reactivity requires use of an excess monomer to be the reagent in a nucleotide elongation reaction. Also, it is associated with defects in that confirmation of the progress status of the reaction in an intermediate stage, analysis of intermediate structure and the like are difficult.
On the other hand, the liquid phase synthesis requires complicated treatments such as column purification and the like, and a large-scale and rapid synthesis of about 20 mer chain length morpholino oligonucleotide, which is utilizable as an antisense pharmaceutical product, has been difficult.
In recent years, a synthetic method using hydrophobic group-linked nucleoside, pseudo solid phase-protected nucleoside and the like has been reported as an attempt to solve the respective defects of the liquid phase method and the solid phase method (see patent documents 6, 7). However, synthesis of morpholino oligonucleotide different in the reaction pathway and the reaction itself from those of oligonucleotide synthesis is not described or suggested.